Why a high level of redundancy would be designed into a network?

Answer 1

Redundancy allows recovery from errors. Networks, like all hardware, can have hardware failures. Computer networks sometime have many components and hardware failures can include something as simple as switching off the power or as annoying as a fishing boat dragging up and breaking an ocean cable.

However, networks also have a lot of soft errors. The most common kind are from congestion, where too much data tries to go on one route. In order to cope with this the switches generally just discard the overload. It is up to the senders and receivers to realize there are errors, and retry later or with some other route. Either way, this works better if we have some redundancy, something extra, built into the network.

Whether due to hardware or due to congestion, networks always have significant levels of error, and so we have learned to use redundancy to allow us to recover from errors. Modern computers are increasingly using systems of redundancy to allow imperfect devices to cooperate to provide a nearly perfect service.